An integrated optical circuit employs optical waveguides to transmit light around the circuit and to connect to external optical waveguides such as optical fibres. The integrated optical waveguides and/or optical fibres may be of different cross-sectional size so there is a need for means to provide a transition from a waveguide of relatively large cross-section to a waveguide of smaller cross-section. A variety of devices have been proposed for this purpose but they tend to be relatively complex and/or difficult to fabricate.
This invention aims to provide a tapered rib waveguide which is of relatively simple construction, is relatively easy to fabricate and which provides a low-loss transition from a large cross-section to a smaller cross-section.
It should be noted that terms such as "upper", "lower", "laterally" etc. used herein are used in a relative sense, i.e. relative to the orientation of the apparatus shown in the accompanying drawing, and are not intended to imply any orientation with respect to the force of gravity.